Treatment of metallurgical dusts containing arsenic



Sept. 30, 1941 F. R. ARCHI BALD TREATMENT OF METALLURGICAL" DUS'ISCONTAININQARSENIC Filed May 8, 1940 SOLUTION STORAGE fi' fl l l H M IXING- TAN K I LIHF-CGNTAINIMG "Am/AL 1 FLOTATION TA/im e f -ro R CELLS I Il Iconrcsmnr: I I I M'VEIYTO/P:

FREDERICK R. ARCH/BALD ATTORNEX Patented Sept. 30, 1941 TREATMENT OFMETALLURGICAL DUS'IS CONTAINING ARSENIC Frederick Batcliife Archibald.Duparquet, Quea bee, Canada, assignor to Beattie Gold Mines (Quebec)Limited, Duparquet, Quebec, Canada Application May 8, 1940, Serial No.333,941

9 Claims. (Cl-.209-166) This invention relates to the recovery ofarsenious oxide (AS203) in relatively pure form, and particularlyv to a.convenient and economical method of recovering AS203 in marketable formfrom dust collected in roasting, smelting or other like metallurgicaloperations.

m the initial stage it is best to incorporate a small portionof'ordinary coal oil or kerosene The usual procedure of treatingdust-containing gases is to collect the dust by the Cottrell orother'system. Units are maintained at temperatures adapted to thematerials to be collected. In collecting arsenic the gases are cooled toa temperature of 250-300 F. This procedure offers dimculties inrecovering arsenic. The separation is not complete. There isoverlappingof the stages and impurities remaining in the arsenic fraction makepurification necessary where a substantially pure arsenious oxide isrequired. I

The object of the present invention is to provide for more completerecoveryof arsenious oxide from furnace gases, so as to avoid its escapewith the gases to the atmospherewith the attendant danger to animal. andplant life, and at the same time to insure a larger recovery of v thearsenic in a marketable form. Another ob-.

collection system for collecting the arsenic, thus providing a compositedust from which the arsenious oxide may be recovered in substantia pureform.

in the water with which the dust is agitated. This insures flotation ofthe arsenic in this stage, but as the aqueous solution becomes more orlessconcentrated with A820: and SO: the kerosene is unnecessary. Duringreuse the treating solution becomes substantially saturated with AsrOaand substantial SO: and some iron go into solution. This solutionconstitutes the flotation reagent. In order to avoid excessiveaccumulation of sulphuric acid inthe solution, the latter is treated asrequired with lime or the like. Any convenient mill product containingcalcite may be used. The cyclic solution may contain 6% H2804. In caseswhere the dusts do not provide the solution with sulphuric acid it maybe added as such.

The operation of the method is illustrated in Ellie :ccompanying drawingwhich shows a flow ee In cyclic operation the dust from the Cottrell.precipitators or other separators is mixed with the aqueous solutioncontaining arsenic and passed through the flotation cells. Theconcentrates are filtered and the fllter cake may be washed then driedfor shipment. The amount of wash water used will be governed by thatlost or smelter ifit contains useful products, as for Before thefurnace'gases enter the dust collection system their temperature isreduced, by the introduction of air or preferably water in the form of aspray, to say 250 to 300 F., and the cooled gases are then passedthrough the successive units of the dust collecting system; This exampleifa lime-containing mill concentrate is usedto neutralize the excessacid in the solu-- tion. The filtrates are returned to, the solutionstorage tank for recirculation.

The following illustrate results obtained:

(1) Using its treating agent a solution pre-- pared by agitating a dustwith water and a small amount of coal oil, 390 grams of cold dust from aQottrell precipitator were passed in two 1 lots through a flotationcell. The results were as follows:

Percent f Weight M Heads 7 Concentrate 22 Filtrate 5700 1.275

r The concentrate was retreated with the filtrate and the recleanedconcentrate contained 96.0% As202. After the solution has been reusedsev- (6181 times no addition of coal oil or other agent is necessary.

(2) 250 grams of dust were treated with a solution as above and furtherportions of equal amount were successively treated with the filtratefrom the previous run with the following results:

' The solution following the twelfth cycle contained in grams per litre16.5 AS203, 27.2 total S03, 1.80 CaO and 3.64 Fe. After treating thissolution with lime-containing tailings it contained in grams per litreA5203 8.5, CaO 0.9, total S02 4.25 and Fe 1.36. n

(3) Without the use of coal 011 6000 grams of cold Cottrell dust wereagitated with water until the solution contained substantially 6% H2804and this solution gave a concentrate containing 96. As2O2. The filtratecontained 23.4 grams per ,litre of A5203 andafter treatment with alime-containing concentrate contained 8.5 grams per litre of AS203 and9.3 grams per litre of The cyclic use of the treating solution avoidsloss of As2O3 and the purity of the final product may be substantiallyincreased by retreatment. The return of the flotation tailings to theroaster avoids loss therein and when a normal mill product is employedfor removing sulphate from the solution no extra load is imposed on themill operation.

I claim: a I

l. A method of treating metallurgical dust containing S03 and arsenicoxide for the recovery of the latter in substantially pure form whichcomprises subjecting the dust to a froth flotation operation in thepresence of a solutionformed by agitating such dust in the presence ofwater. v

2. A method of treating metallurgical dust containing S03 arsenic oxidewhich comprises agitating such dustin the presence of water to form aflotation reagent and subjecting the dust with said reagent to a frothflotation operation to float and concentrate the arsenic oxide therein.

3. A method as set forth in claim 2 wherein the dust is agitated in thepresence of water and coal ofl to form the flotation agent.

4. A method of concentrating the arsenic oxide in metallurgical dustscontaining it which vconiprises passing the dust through a frothflotation cell with an aqueous solution containing arsenic oxide andsulphuric acid to float the AS202 and recovering the concentrate.

5. A cyclic method for recovering arsenic oxide in substantially pureform from metallurgical dusts containing S03 and arsenic oxide whichcomprises mixing the dust with a solution containing arsenic oxide,passing the mixture through a froth flotation cell to float the arsenicoxide, filtering the concentrate and returning the filtrate for reuse inthe circuit.

6. A cyclic method for recovering substantially pure arsenic oxide frommetallurgical dusts containing it and S02 which comprises mixing thedust with a solution formed by agitating such lurgical dusts containingS0: and a substantial proportion of arsenic oxide which comprisesagitatlng dust with water to forms. flotation agent,-

subjecting dust to treatment in a froth flotation cell with said agentto float and concentrate the arsenic oxide, filtering the concentrate,treating the filtrate with lime-containing material and rettu'ningthetreated filtrate to the circuit.

9. A method as set forth in claim 6 wherein sulphuric acid is added tothe solution formed by agitating the dust with water.

FREDERICK RATCLIFFE ARCHIBALD.

